1. Field of Invention
The present invention relates to a method of producing light-weight alumina particles. The light-weight alumina particles can be used for aggregate materials, refractory brick materials, electrically conducting materials, heat-conducting materials, and so on.
2. Related Art
As the background-art method of producing light-weight alumina particles, there is a method in which high-pressure air is blown on molten alumina (Al2O3) so that alumina particles 1 having hollow portions 1A as shown in FIG. 5 are produced (JP-A-52-50987). The hollow alumina particles formed by blowing air in the aforementioned manner has a particle size in a range of from 200 xcexcm to 4000 xcexcm in accordance with the physical properties, or the like, of the molten alumina.
The particle size of the alumina particles produced by the aforementioned method was, however, ununiform in a range of from 2000 xcexcm to 4000 xcexcm. That is, it was difficult to control the particle size of the alumina particles to be produced. Further, in the method of producing alumina particles by blowing high-pressure air, there was a problem that it was impossible to form alumina particles having a smaller particle size than 2000 xcexcm.
Particularly, the particle size of alumina particles has an influence on mechanical strength. If the particle size of alumina particles is not smaller, for example, than 2000 xcexcm, interparticle gaps become so large that the mechanical strength is reduced. If the particle size of alumina particles is contrariwise too small, the fluidity of particles becomes so low that moldability is worsened. Further, if the particle size is small, the density of particles becomes so high that light weight is not achieved.
It is, therefore, important to set the particle size of alumina particles at a predetermined value smaller than 2000 xcexcm and make the alumina particles uniform at the predetermined particle size for the purpose of using the alumina particles for aggregate materials, refractory brick materials, and so on, requiring great mechanical strength.
The problem to be solved by the present invention is what means should be taken to obtain a method of producing light-weight alumina particles with the particle size controlled well to be made uniform.
According to a first aspect of the present invention, there is provided a method of producing light-weight alumina particles, comprising the steps of: preparing a mixture of core particles which are formed from a light-weight material so as to be used as nuclei of objective particles and so as to have a particle size in a range of from 1 xcexcm inclusive to 2000 xcexcm exclusive and slurry which contains fine alumina powder; drying the mixture by removing water content of the mixture; and baking the dried mixture at a temperature in a range of from 1200xc2x0 C. to 1500xc2x0 C. to thereby sinter alumina on surfaces of the core particles.
In a first aspect of the present invention, the particle size of the core particles as nuclei of objective particles, that is, of light-weight alumina particles, is set at a value in a range of from 1 xcexcm inclusive to 2000 xcexcm exclusive, so that the particle size of the light-weight alumina particles after baked can be set at a value smaller than 2000 xcexcm. Accordingly, in the case of using the light-weight alumina particles as aggregate materials or light-weight brick materials, the great mechanical strength can be ensured. Further, because the particle size of the light-weight alumina particles is set at 1 xcexcm or more, the high fluidity for molding can be ensured.
According to a second aspect of the present invention, in the method of producing light-weight alumina particles of the first aspect of the present invention, the core particles are size-enlarged sludge particles. In this invention, use of size-enlarged sludge particles as the core particles makes it possible to form light-weight alumina particles and reduce the cost of production. Further, in this invention, an attempt to use sludge can contribute to solution of environmental problems.
According to a third aspect of the present invention, in the method of producing light-weight alumina particles of the first aspect of the present invention, the particle size of the core particles, that is, of the size-enlarged sludge particles are set at a value in a range of from 1 xcexcm to 1000 xcexcm. In this invention, the particle size of the core particles constituted by the size-enlarged sludge particles is set at a value in a range of from 1 xcexcm to 1000 xcexcm, so that the ratio of the weight of the size-enlarged sludge particles in the objective particles (light-weight alumina particles) is lowered. Accordingly, the specific gravity of the objective particles is reduced so that the weight of the same is reduced.
According to a fourth aspect of the present invention, in addition to the effect of the first aspect of the present invention, the specific gravity of the light-weight alumina particles can be reduced more effectively so that the weight of the objective particles can be reduced more largely because the core particles are constituted by small resin balls or styrene foam particles which are low in specific gravity.
According to a fifth aspect of the present invention, in the method of producing light-weight alumina particles of the fourth aspect of the present invention, the particle size of the core particles is in a range of from 20 xcexcm inclusive to 2000 xcexcm exclusive. In this invention, light-weight alumina particles using small resin balls or styrene foam particles as the core particles and having a particle size of 2000 xcexcm or less can be produced.
According to a sixth aspect of the present invention, in the method of producing light-weight alumina particles of any one of the first to fifth aspect of the present invention, the core particles are left as residues in the inside of resulting particles after the baking. In this invention, the core particles are left as residues in the inside of the objective particles, so that substantial reduction of the weight of the core particles can be achieved. Accordingly, the specific gravity of the objective particles (light-weight alumina particles) can be reduced more effectively. Further, the core particles are left as residues in the inside of the objective particles, so that the great mechanical strength can be ensured.
According to the seventh aspect of the present invention, in the method of producing light-weight alumina particles of fourth or fifth aspect, the core particles are left as small resin balls or as foam particles in the inside of resulting particles after the baking. In this invention, the core particles are left as small resin balls or as foam particles, so that the specific gravity of the objective particles can be reduced.
According to an eighth aspect of the present invention, in the method of producing light-weight alumina particles of any one of the first through the seventh aspect, the thickness of sintered alumina on the surfaces of the core particles is in a range of from 1 xcexcm to 200 xcexcm. In this invention, the thickness of sintered alumina is set at a value in a range of from 1 xcexcm to 2000 xcexcm, so that the great mechanical strength of the objective particles can be ensured. Incidentally, the thickness of sintered alumina can be controlled by adjustment of the amount of fine alumina powder contained in the slurry.